1. Technical Field
The present invention relates to a remotely operated multi-zone packing system used in multi-zone gravel pack, frac pack, and similar applications in oil field wells. Specifically, the present invention allows for remote operation of gravel pack, frac pack, or similar assemblies in multi-zone applications, thus eliminating the requirement to physically relocate a work string to each zone of interest to accomplish various phases of the completion.
2. Description of Related Art
Gravel pack assemblies and frac pack assemblies are commonly used in oil field well completions. A frac pack assembly is used to stimulate well production by using liquid under high pressure pumped down a well to fracture the reservoir rock adjacent to the wellbore. Propping agents suspended in the high-pressure fluids (in hydraulic fracturing) are used to keep the fractures open, thus facilitating increased flow rates into the wellbore. Gravel pack completions are commonly used for unconsolidated reservoirs for sand control. Gravel packs can be used in open-hole completions or inside-casing applications. An example of a typical gravel pack application involves reaming out a cavity in the reservoir and then filling the well with sorted, loose sand (referred to in the industry as gravel). This gravel pack provides a packed sand layer in the wellbore and next to the surrounding reservoir producing formation, thus restricting formation sand migration. A slotted or screen liner is run in the gravel pack which allows the production fluids to enter the production tubing while filtering out the surrounding gravel.
A typical single-zone gravel pack completion is illustrated in FIG. 1. FIG. 1 is a schematic cutaway representation showing a perforated wellbore casing 2 with perforations 12 shown extending into a single zone of interest 10. Within the wellbore casing 2 a tube 4 has been placed on which is attached a screen 6. The gravel 8 is shown packed into the perforations 12 in the zone of interest 10 and surrounding the screen 6. The gravel 8 is an effective filter of formation fluids, because the formation sand, which would otherwise flow with the production fluid, is largely trapped at the interface with the gravel 8.
One specific type of gravel pack procedure is called a squeeze gravel pack. The squeeze gravel pack method uses high pressure to xe2x80x9csqueezexe2x80x9d the carrier fluid into the formation, thereby placing gravel 8 in the perforation tunnels 12 of a completed well and the screen/casing annulus. The frac pack method is very similar, except the xe2x80x9csqueezexe2x80x9d is carried out at even higher pressures with more viscous fluid in order to fracture the reservoir rock. Consequently, the down-hole assembly used for these two procedures is frequently the same, and the procedures will be discussed as examples interchangeably in this disclosure.
A typical gravel pack or frac pack assembly is presently run into the well on a work string. The work string is commonly a length of drill pipe normally removed from the well once the packing job is complete. The work string assembly contains a means for setting the packer and a crossover tool to redirect the treatment from within the work string into the formation. This is illustrated by FIG. 2, which shows a schematic cutaway of a basic frac pack assembly for a single zone of interest 210 application. At the upper portion of the assembly the work string is a single tube or pipe 214 (which is also referred to herein as the inner tubing). Further down the assembly this single tube 214 is attached to and enclosed by a middle concentric tube 216. The now inner tube 214 and middle tube 216 are integral to the work string and can be moved vertically through the wellbore annulus 202 by manipulation at the rig level. The middle tube 216 is initially attached to or pinned to an outer concentric tube 204 when the assembly is landed in the well. Immediately above the point where the middle tube 216 and the outer 204 begin to interface concentrically are seal points 218, 230, providing pressure seals between the middle concentric tube 216 and the outer concentric tube 204. Once the assembly is landed and set in place, the temporary attachment between the middle tube 216 and the outer tube 204 can be broken, for example by applying tension to a shear pin by pulling the middle tubing 216 upward. The seal points 218, 230 provide pressure isolation between the middle tubing 216 and the outer tubing 204 even as the work string is moved up and down in the assembly.
Attached to the outer tubing 204 is a hydraulic set packer 220. When xe2x80x9cset,xe2x80x9d a procedure that will be described momentarily, the hydraulic set packer 220 provides a complete seal between the outer tubing 204 and the wellbore casing 202. Below the hydraulic set packer is a fluid crossover port 240, formed by passages through the inner tubing 214 and the concentric middle tubing 216, which allows fluid to crossover from the inner tubing 214 through the concentric middle tubing 216 without coming into physical contact with any fluid that may be passing through the annulus between the inner tubing 214 and the concentric middle tubing 216. A gravel pack port 224, which is opened and closed with a closing sleeve 226, which is operated by a shifting tool (not shown), provides communication for fluid exiting the crossover port 240 into the wellbore annulus 202. This gravel pack port 224, although shown in the open position, may be initially in the closed position with the closing sleeve 226 sealing the port 224 when the assembly is landed in the well. In the closed position, fluid transported down the inner tubing 214 is diverted by a plug 236, passes through the crossover port 240, and is isolated between the hydraulic set packer 220 and a seal 230 located below the port 224. Thus, pressure can be built up inside this isolated segment of the outer tubing 204. The packer 220 is hydraulically actuated or xe2x80x9csetxe2x80x9d by applying fluid pressure until the outer tubing 204 is pressure isolated by the packer""s 220 seals within the wellbore annulus 202.
After the packer 220 is set, the gravel packing or frac packing job can be initiated by opening the gravel pack port 224 by shifting open the closing sleeve 226. This is typically accomplished by physically manipulating the closing sleeve 226 with a shifting tool (not shown) attached to the exterior of the middle tubing 216 by raising or lowering the work string (which consists of the inner tubing 214, the middle tubing 216, and all integral components shown in FIG. 2). Once the closing sleeve 226 opens the port 224, the proppant for the gravel pack or frac pack completion is pumped down the inner tubing 214, through the crossover port 240, out the gravel pack port 224, and into the wellbore annulus 202, as indicated by flow arrows 250 in FIG. 2. Below the closing sleeve 226 and gravel pack port 224, the outer tubing 204 comprises a screen or slotted liner 206, similar to the screen 6 illustrated in FIG. 1. Therefore, during the xe2x80x9cfrac jobxe2x80x9d the proppant is forced into the perforations 212 of the wellbore casing 202 and begins to fill the cavity between the screen 206 and the wellbore casing 202. The carrier fluid 250 for the gravel, after being filtered by the screen 206, may be circulated through the annulus between the inner tubing 214 and the concentric middle tubing 216, which has an open end 232 inside the screen 206 in a single zone of interest application. The fluid 250 goes past a ball 234 near the bottom opening 232 of the middle tubing 216, which acts as a check valve preventing fluids from back flowing from the annulus between the inner tubing 214 and the concentric middle tubing 216 back into the screen. The circulation of the carrier fluid exits through a port 238 above the seal point 218.
The gravel pack procedure becomes more complex when it is necessary to accomplish a frac pack or gravel pack completion on multiple zones of interest within the same wellbore. FIG. 3 illustrates a schematic cutaway of a typical prior art multi-zone frac pack assembly used for this purpose. FIG. 3 shows two zones of interest 310, 311 isolated by hydraulic set packers 320, 321, 322. Packers 321 that separate zones of interest 310, 311 are typically called isolation packers, while the packer 322 which is set below the last zone of interest in the wellbore is known as a sump packer and is set before landing the gravel pack assembly. Common to each zone of interest 310, 311 on the multi-zone assembly is a gravel pack port 324, 325 with associated closing sleeve 326, 327 and a screen 306, 307. The screens 306, 307 are placed opposite each zone of interest 310, 311. As with the single zone of interest assembly illustrated by FIG. 2, the multiple zone assembly comprises inner tubing 314 and middle tubing 316, which are attached above the top packer 320. Outer tubing 304 is shown which is initially fixed in position relative to the other concentric tubes (work string) when landing in the well. Although the upper gravel pack port 324 is shown closed while the lower gravel pack port 325 is shown open in FIG. 3 for illustrative purposes, all of the gravel pack ports 324, 325 are initially in the closed position when the assembly is landed in the well.
To begin the frac pack or gravel pack completion, each of the isolation packers 320, 321 must be set. This is accomplished by starting at the lowest zone 311 to be treated with the crossover tool 340 in the position illustrated by FIG. 3. Since the gravel pack port 325 is initially closed, fluid 350 pumped down the inner tubing 314 is diverted by a plug 336 and flows through the crossover port 340 into the outer tubing 304, where it is contained between seals 331 and the packer 321. Increasing the fluid pressure thereby actuates or xe2x80x9csetsxe2x80x9d the hydraulic set packer 321. The crossover port 340 is then raised to the next zone 310 by lifting the entire work string (comprising both the inner tubing 314 and the middle tubing 316) in order to set the next packer 320 by the same method. A series of bore seals 317, 318, 319 ensure a proper pressure seal between the middle tubing 316 and the outer tubing 304 while the work string is manipulated.
Once all of the packers 320, 321 have been set, the crossover port 340 is returned to the lowest zone of interest 311 in order to begin the packing stage. Again, this is accomplished by physically lowering the entire work string. All of the gravel pack ports 324, 325 are now in the open position by virtue of, for example, the actuation of a closing sleeve 326, 327 by a shifting tool (not shown). With the crossover port 340 located in the lowest zone of interest 311, proppant 350 is forced from the inner tubing 314, through the crossover port 340, out the open port 325, and into the wellbore annulus 302. The return fluid 350 xe2x80x9ccirculatesxe2x80x9d by traveling through (and is filtered by) the screen 307, into the open end 332 of the middle tubing 316, past the ball 334 and plug 336, through the annulus between the inner tubing 314 and the concentric middle tubing 316, and out the exit port 338, just as in the single zone assembly shown in FIG. 2. Once the packing job is completed in the lowest zone of interest 311, the crossover port 340 is moved to the next zone of interest 310 (by raising the work string) to accomplish a similar procedure, and so on until all zones are completed.
Although FIG. 3 shows only two zones of interest 310, 311, the procedure is the same, and the fixed assembly components (packers, gravel ports, closing sleeves, and screens) are simply duplicated, regardless of the number of zones treated during the packing job. Isolation packers between the zones are set separately by pulling up the work string, and then a packing job is completed on each zone separately by physically placing the crossover port 340 within the zone to be treated and opening the adjacent gravel pack port.
The physical manipulation of the work string up and down through the outer tubing 304 and wellbore casing 302 poses several practical problems with the prior art multi-zone assemblies. The proppants mixed in the fluids 350 used in these applications are extremely abrasive and erosive. The tubing 314, 316 illustrated in FIG. 3 is, of course, not a continuous piece of tubing. Rather, the tubing 314, 316 is made up of individual segments with connections and seals located at the intersection of each segment. These seals are subject to wearing as the work string is moved up and down in such an erosive environment. Consequently, the seals are prone to failure thus compromising the integrity of the assembly. There is also the potential that the work string might get stuck while being moved up and down to accomplish various phases of the completion. The need to physically manipulate the crossover port 340 up and down to the various zones of interest, each time taking steps to insure proper placement of the port 340, is also an involved procedure requiring additional rig time and, consequently, additional cost to the completion job.
A need exists, therefore, for a multi-zone pack assembly that can be remotely activated without the necessity of physically raising and lowering the work string and crossover tool to each zone of interest. Such invention would greatly reduce the wear on the tubing seals and eliminate the potential of the work string getting stuck within the outer tubing during the packing job. Such invention could also save time and completion related expenses by simplifying the steps required to perform each stage of the completion.
The present invention relates to an improved multi-zone gravel pack, frac pack and like assemblies that operate without the necessity of raising and lowering a working string and crossover tool to various zones of interest. The invention uses the unique design of having a crossover tool on the working string collocated at every zone of interest combined with remotely activated closing tools.
One embodiment of the invention discloses a circulation valve, which allows for carrier fluid to either circulate after passing through the screen or flow through from a lower portion of the assembly, or be xe2x80x9creverse circulatedxe2x80x9d back up the workstring, and a remotely activated crossover port at each zone of interest. The closing sleeve on the gravel pack port allowing access to the wellbore annulus is opened and closed through use of traditional closing tools and minor manipulations of the work string. However, the work string does not need to be raised and lowered as between zones of interest. Therefore, the wear and tear on the work string is greatly reduced and the time required to perform the setting of each isolation packer as well as the gravel pack completion in each zone is reduced.
Another embodiment of the invention requires no movement of the work string relative to the outer tubing. Again, in the circulation embodiment, there is a crossover tool collocated at every zone of interest. Rather than using a closing sleeve on the gravel pack port and a circulation valve, the second embodiment uses an iris valve or other similar means to divert flow within the washpipe and a remotely actuated closing sleeve at the gravel pack port.
The invention is versatile and can be tailored to meet the requirements of each specific well completion. By eliminating the need to move the work string and single crossover tool to each zone of interest in order to set each individual packer and later perform the gravel pack job for each zone, this invention greatly reduces the wear and tear on the work string seals and eliminates the possibility that the work string might become stuck during physical manipulation. Further, by allowing the stages of a multi-zone packing job to be accomplished simultaneously, and by eliminating the time required to raise and lower the working string, this invention is a great improvement over the prior art in efficiency and cost effectiveness.